Permanent magnet system for focusing an electron beam



F. EDER 3,241,007

PERMANENT MAGNET SYSTEM FOR FOCUSING AN ELECTRON BEAM March 15, 1966Filed Dec. 16, 1963 United States Patent 3,241,007 PERMANENT MAGNETSYSTEM FOR FOCUSING AN ELEQTRON BEAM Felix Eder, Munich, Germany,assignor t0 Siemens &

Halske Aktiengesellschaft, Berlin and Munich, Germany, a corporation ofGermany Filed Dec. 16, 1963, Ser. No. 331,011 Claims priority,application Germany, Dec. 21, 1962, S 83,006 5 Claims. (Cl. 317200) Theinvention disclosed herein is concerned with a permanent magnet systemfor the focused guiding of an electron beam, especially for travelingwave tubes, comprising permanent magnets arranged axially symmetricallywith respect to the electron beam and having pole pieces of soft ironwhich are successively disposed in the direction of the electron beamand magnetically interconnect poles of the permanent magnets ofidentical polarity lying mutually oppositely in planes extendingperpendicularly to the electron beam direction, the respective polepieces having bores formed therein centrally thereof, for receiving thedischarge vessel and being, in longitudinal section through the magnetsystem, of a width which is in the region of the respective bores lessthan at regions thereof which are disposed adjacent the magnets.

Permanent magnet systems of this general type, for producing a periodicdirectionally alternating magnetic field, are known. The pole pieces aremade narrower in the region of the bore for receiving the dischargevessel than in the vicinity of the magnets so as to obtain from themagnets a magnetic flux as great as possible, such flux being determinedby the cross section of the portions of the pole pieces which arearranged adjacent the magnets. These known pole pieces are produced bymilling a forced blank and subsequently grinding it to its final shape.Such production entails great expenditure due to the required millingand grinding operations. Difficult and elaborate milling and grindingoperations are particularly required in cases in which the pole piecesare to receive a discharge vessel having a diameter which exceeds thetransverse dimension of the pole pieces in the vicinity of the magnets.In such a case, the forged blank must be machined so that the polepieces are, as seen in the electron beam direction, centrally wider thanin the vicinity of the magnets so as to enable provision, centrally ofthe pole pieces, of a correspondingly large bore for receiving thedischarge vessel.

The present invention proposes to avoid the above indicated difiicultiesoccuring in connection with a permanent magnet system of the initiallydescribed type, by the provision of pole pieces made respectively from aflat cross-sectional rectangular strip of soft iron, such strip beingtwisted with respect to its central portion by 90 about its longitudinalaxis, such that the central portion thereof, in which is formed thebore, is displaced by 90 with respect to the longitudinal plane of theuntw-isted portions of the strip.

The advantage of the permanent magnet system according to the inventionresides in that the pole pieces can be produced without resorting tomilling and grinding operations. All that is necessary is to providecrosssectionally rectangular metal strips with a bore formed thereincentrally thereof and to twist such a prefabricated strip twice. Thetwisting is effected by a simple forging operation.

The various details and features of the invention will appear from theappended claims and from the description of an embodiment thereof whichis rendered below with reference to the accompanying drawing.

3,241,007 Patented Mar. 15, 1966 FIG. 1 shows a side View of a polepiece of the permanent magnet system according to the invention;

FIG. 2 represents the pole piece as seen from the front, that is, in theelectron beam direction;

FIG. 3 illustrates the front view of a permanent magnet system accordingto the invention, for producing a periodic directionally alternatingmagnetic field; and

FIG. 4 shows the system in section taken along the lines A-B of FIG. 3.

Referring now to FIGS. 1 and 2, the pole piece 1 consists of acr-oss-sect-ionally rectangular metallic strip of uniform thicknesshaving a bore 2 formed therein centrally thereof, for receiving adischarge vessel, and being by a forging operation twisted about itslongitudinal axis by with respect to its central portion. The width ofthe pole piece, along a longitudinal section through the magnet system,is by this construction narrower in the region of the bore 2 than in theouter portions thereof (FIG. 1) while having, as seen in the electronbeam direction (FIG. 2), a central portion which is wider than the outerportions thereof. The outer portions 4 and 4' of the pole piece are inthe illustrated example twisted in the same sense with respect to thecentral portion in which is formed the bore 2. However, the twisting mayalso be effected in opposite sense.

As seen from FIGS. 3 and 4, the magnets 5, 6, 7, 8 are arrangedsymmetrically to the axis of the electron beam, thus forming the sidesof a square. Identical poles of the magnets, which are magnetized incircumferential direction of the square, coincide at the corners of thesquare. Accordingly, oppoistely disposed corners of the square have thesame polarity. These corners are interconnected alternately in verticaland horizontal direction by pole pieces 1 and 1 made as shown in FIGS. 1and 2. The pole pieces 1 and 1, respectively, which are successively inalignment, border directly one on the other adjacent the magnets. A softiron ring 9 is provided in the respective bores 2 of the pole pieces 1and 1, such ring serving for compensating disturbances in the rotationsymmetry of the periodic magnetic field, which may be caused in theevent that the twisted planes of the pole pieces 1 and 1' do not extendexactly perpendicularly with respect to an another.

The invention is not inherently limited to a permanent magnet systemaccording to FIGS. 3 and 4. It is, for example, possible to use a polepiece such as shown in FIGS. 1 and 2 in connection with a permanentmagnet system in which the magnetic field does not change its directionperiodically.

Changes may be made Within the scope and spirit of the appended claimswhich define what is believed to be new and desired to have protected byLetters Patent.

I claim:

1. A permanent magnet system for the focused guiding of an electronbeam, especially for travelling Wave tubes, comprising permanent magnetsarranged axially symmetrically along the path of such an electron beamand having pole pieces of soft iron which are successively disposed inthe direction of the electron beam path and magnetically interconnectmagnetic faces of identical polarity disposed in planes extending in thedirection of the electron beam path, the respective pole pieces havingbores formed therein centrally thereof for receiving a discharge vesseland being, in longitudinal section through the magnet system, of a widthwhich is in the region of the respective bores less than at regionsthereof which are disposed adjacent the magnets, thereby characterizedthat each respective pole piece is formed of a fiat cross-sectionalrectangular strip of soft iron having a bore formed in the centralportion thereof, the outer portions of said strip which extend from saidcentral portion being twisted by 90 with respect thereto so that thecentral portion in which is formed said bore is displaced by 90 withrespect to the longitudinal planes of the respective outer portions.

2. A permanent magnet system according to claim 1, wherein the outerportions of said strip are twisted in identical sense with respect tosaid central portion.

3. A permanent magnet system according to claim 2, comprising a ring ofsoft iron which is inserted in said bore.

4. A permanent magnet system according to claim 3, wherein saidpermanent magnets are arranged so as to form in planes extendingperpendicularly to the electron beam a quadratic square wherein poles ofidentical polarity are in circumferential direction mutually adjacentlydisposed, said pole pieces interconnecting alternately oppositelypositioned corners of the square so References Cited by the ExaminerUNITED STATES PATENTS 3,061,754 10/1962 Kajihara.

FOREIGN PATENTS 601,511 8/1934 Germany.

BERNARD A. GILHEANY, Primary Examiner.

LARAMIE E, ASKIN, Examiner.

1. A PERMANENT MAGNET SYSTEM FOR THE FOCUSED GUIDING OF AN ELECTRONBEAM, ESPECIALLY FOR TRAVELLING WAVE TUBES, COMPRISING PERMANENT MAGNETSARRANGED AXIALLY SYMMETRICALLY ALONG THE PATH OF SUCH AN ELECTRON BEAMAND HAVING POLE PIECES OF SOFT IRON WHICH ARE SUCCESSIVELY DISPOSED INTHE DIRECTION OF THE ELECTRON BEAM PATH AND MAGNETICALLY INTERCONNECTMAGNETIC FACES OF IDENTICAL POLARITY DISPOSED IN PLANES EXTENDING IN THEDIRECTION OF THE ELECTRON BEAM PATH, THE RESPECTIVE POLE PIECES HAVINGBORES FORMED THEREIN CENTRALLY THEREOF FOR RECEIVING A DISCHARGE VESSELAND BEING, IN LONGITUDINAL SECTION THROUGH THE MAGNET SYSTEM, OF A WIDTHWHICH IS IN THE REGION OF THE RESPECTIVE BORES LESS THAN AT REGIONSTHEREOF WHICH ARE DISPOSED ADJACENT THE MAGNETS, THEREBY CHARACTERIZEDTHAT EACH RESPECTIVE POLE PIECE IS FORMED OF A FLAT CROSS-SECTIONALRECTANGULAR STRIP OF SOFT IRON HAVING A BORE FORMED IN THE CENTRALPORTION THEREOF, THE OUTER PORTIONS OF SAID STRIP WHICH EXTEND FROM SAIDCENTRAL PORTION BEING TWISTED BY 90* WITH RESPECT THERETO SO THAT THECENTRAL PORTION IN WHICH IS FORMED SAID BORE IS DISPLACED BY 90* WITHRESPECT TO THE LONGITUDINAL PLANES OF THE RESPECTIVE OUTER PORTIONS.